Propellant-powered fluid jet cutting apparatus and methods of use

ABSTRACT

Apparatus providing at least one high pressure fluid cutting jet and methods employing same. A gas generator powered by a combustible propellant supplies pressurized gas to propel a fluid through at least one nozzle to form a cutting jet suitable for cutting materials such as structural elements. Furthermore, nozzles may be configured to rotate in order to circumferentially sever a tubular structural element. Two or more fluid cutting jets may be configured to intersect, and may be configured to intersect proximate to at least a portion of the periphery of the tubular structural element to be severed.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates generally to apparatus and methods for severing tubing, casing, drill pipe, and other structural elements and materials. More specifically, the present invention relates to an apparatus and method for cutting structural elements with a fluid cutting jet powered by a solid propellant-powered gas generator.

[0003] 2. State of the Art

[0004] As known in the art, one of the first steps in oil and gas production is drilling a wellbore, or borehole, into the hydrocarbon-bearing formation. Boreholes are commonly drilled into subterranean formations by applying rotary motion to a cutting instrument, or rotary drill bit, by way of one or more of a rotary table, top drive, drilling rig, or downhole motor, which penetrates and removes the subterranean formation material. The rotary drill bit is generally either a fixed cutter (drag) or rolling cone (tri-cone) type drill bit, as known in the art, depending on the formation, the drilling equipment, and drilling conditions. The drill bit is threadedly connected to a pipe structure comprised of threadedly connected pipe sections that extend upwardly to the surface of the formation. The pipe structure, together with other components which may be attached to the bottom end or in between the pipe sections for drilling the borehole are collectively called a drillstring.

[0005] Some subterranean formations may be sensitive to the drilling process, or they may lack mechanical integrity when a borehole is drilled therein due to the pressures experienced within the borehole, or other conditions within the formation. Such a formation may occasionally swell, i.e., dilatation of a rock formation due to changing pressure, or slough into the open borehole during drilling. If the sloughing or swelling is severe enough, the drillstring may become lodged in the borehole in such a way as to prevent further drilling, or removal of the drillstring from the borehole by applying a force at the end of the drillstring that exits the surface of the formation.

[0006] If it is determined that removal of the drillstring is not possible by applying a force at the end of the drillstring that exits the formation because it has become stuck, it is often desirable to attempt to remove as much of the drillstring as possible from the borehole. Removal of the greatest possible amount of drillstring from the borehole both reduces the amount of drillstring abandoned in the borehole, and reduces the amount of borehole that would have to be drilled again if the drilling contractor should choose to attempt to redrill the borehole to the same target subterranean formation.

[0007] After a borehole is successfully drilled to the target subterranean formation and the drill string is removed, a protective pipe called a liner or casing may be typically set into the borehole to a predetermined depth. The casing is generally steel and is used to form a hydraulic seal between different subterranean formations penetrated by the borehole as well as to ensure the integrity of the borehole, i.e., so that it does not collapse. Another reason for installing casing is to isolate different geologic zones, e.g., an oil-bearing zone from an undesirable water-bearing zone. Sometimes while the casing is being lowered into the borehole it can become stuck from some of the same causes which may cause the drillstring to become stuck. In order to complete the borehole it is typically necessary to remove as much casing as possible and redrill the borehole to the depth of the target formation.

[0008] Once the casing is inserted into the borehole, it is then cemented in place, by pumping cement into the gap between casing and borehole (annulus). By placing a casing in the borehole and cementing the casing to the borehole, then selectively forming holes in the casing, one can effectively isolate certain portions of the subsurface, for instance to avoid the co-production of water along with oil. However, it may be desired to remove casing from boreholes that have produced substantially all of the economically recoverable oil and gas from the subterranean formations penetrated by those boreholes, in an attempt to salvage some of the casing before plugging and abandoning the borehole.

[0009] In still other boreholes, an additional pipe may be inserted coaxially inside the casing. The additional pipe is called a tubing string. The tubing string generally serves the purpose of increasing the velocity of fluids flowing up the borehole so that more dense components of the fluid, such as water, will become entrained in the fluid flow and be carried to the earth's surface, thereby reducing hydrostatic pressure opposing the entry of fluids into the borehole. When a borehole having a tubing string is to be recompleted into a different formation or is to be abandoned, it is usually desirable to remove the tubing string from the borehole. Occasionally the tubing string may become stuck in the borehole, thereby preventing the removal of the tubing string from the borehole.

[0010] In all of the situations described herein in which a tubular structural element, which may be termed “pipe” for convenience, becomes stuck in or is desired to be removed from the borehole, it may prove necessary to sever the pipe above the point at which it is stuck in order to enable recovery of the portion of the pipe which is not stuck.

[0011] Conventional mechanical cutting tools for removing stuck pipe from a borehole have been developed and are relatively well known in the art. Various types of downhole cutting and milling tools have been utilized in the oil and gas industry for removing components from within wellbores including cutting existing casings, for boring through permanently set packers and for removing loose joints of pipes. Typically, a plurality of cutting blades having a suitable hard cutting material, such as carbide, are placed on a body at spaced intervals extending outwardly therefrom. The tool may be placed at a desired location within the wellbore and rotated to cut the intended material, by using the weight on the tool and the rotational speed to determine the cutting speed. One disadvantage to mechanical cutters is that the cutting material wears and must be replaced periodically. In such cases, the cutting tool must be retrieved from the borehole, which results in lost time for the well and/or rig and, thus, increases costs.

[0012] The conventional practice in chemically severing downhole tubular structural elements is to arrange the cutting ports in the cylindrical wall of the cutting head, as disclosed for example in U.S. Pat. No. 4,125,161 to Chammas. The Chammas cutting tool incorporates an anchor sub having a plurality of wedges pivoted on an actuating piston near the upper end of the tool in which gas from a propellant charge displaces an actuating piston to cam the wedges outwardly against the tubing string or other object to be cut. The gas from the propellant charge is employed to force the cutting chemical into contact with a reactant material and then outwardly through the cutting ports. Disadvantageously, as with all chemical cutters, highly reactive and potentially dangerous chemicals (such as bromine trifluoride, a highly reactive acid) are expelled into the borehole in order to cut the tubular structural element and often must be subsequently removed from the borehole. Furthermore, conventional chemical cutting tools are limited to cutting tubular structural elements having a wall thickness of about 0.45 inch or less, and must be maintained at a maximum clearance of about 0.35 inch from the inner wall of the tubular structural element.

[0013] Jet cutters are explosive cutting tools known in the art for severing pipe in a borehole. A jet cutter comprises a charge of high explosive compound in the form of a “shaped” charge configured to, upon detonation, create a “jet” of high pressure, high temperature gas which is directed circumferentially from inside the pipe to cut the pipe. A jet cutter may be actuated by an electrically powered initiator such as a blasting cap. Further, a jet cutter may also utilize thermite or other relatively sensitive explosives. One example of is described as a “JRC Drill Collar Severing Tool,” offered by Jet Research Center, Inc., Alvarado, Tex. The severing tool comprises a plurality of high explosive charges adapted to detonate is a coordinated sequence to generate an extremely powerful cutting jet.

[0014] In addition, because the jet cutter typically utilizes initiation of a short duration, powerful explosive charge, reactive forces may be generated on the cutting tool by the detonation, and may cause the tool to move within the borehole, cables suspending the tool to become tangled, or the cutter and associated equipment to become damaged. Further, it may be difficult to tailor the output of a jet cutter to properly contact the desired area of the tubular component in which it is suspended.

[0015] In addition, there have been attempts to utilize fluid cutting jets for removing stuck drill pipes or casings from a borehole. U.S. Pat. No. 5,381,631 to Raghaven et al. describes a tool for cutting metal casings by way of an ultrahigh-pressure abrasive fluid cutting jet. An ultrahigh pressure pump generates an ultrahigh-pressure fluid stream that may range from 20,000-100,000 psi. that is conveyed by a first feed line to a jet manifold. Further, a second feed line to the jet manifold conveys abrasives that are mixed with the ultrahigh-pressure fluid stream, thereby generating an abrasive fluid stream. The abrasive fluid stream exits the mixing chamber and ultimately exits a nozzle block, forming an abrasive fluid cutting jet for cutting casing elements.

[0016] U.S. Pat. No. 6,155,343 to Nazzal et al. describes a cutting tool that includes a cutting end that is adapted to discharge a high pressure fluid therefrom. A power unit including a series of pressure stages that successively increase the pressure of the fluid until a desired level of pressure has been reaches are used to power the cutting tool. A “pulsar” to pulse the pressure of the fluid before it is discharged through the nozzle as well as an imaging device are also described.

[0017] Both the cutting tool of Nazzal et al. and the cutting tool of Raghaven et al. include relatively complicated fluid pressurizing machinery for creating a suitable fluid pressure for the cutting tool to function effectively. In addition, the machinery to create suitable pressure sources for the Raghaven and Nazzal inventions may not be easily configured for supplying different pressures for different operating conditions or for cutting different materials. Further, while it would be desirable to effectuate fluid jet cutting in remote locations where power is not readily available and transportability becomes a significant issue, the state of the art fails to provide such a capability.

[0018] In view of the foregoing, a cutting tool utilizing high pressure fluid which improves on conventional cutting tools and eliminates some of their respective disadvantages would be desirable.

BRIEF SUMMARY OF THE INVENTION

[0019] The present invention comprises an apparatus for cutting into, and through, a structural element, including without limitation cutting through the wall of a tubular structural element, using at least one high pressure fluid cutting jet and methods employing same. Fluid cutting jet, as used herein, refers to a fluid jet which possesses cutting ability due, in part, to its velocity and/or its momentum.

[0020] More specifically, the apparatus of the present invention comprises a gas generator powered by a propellant, such as a combustible propellant, that supplies pressurized gas to propel a fluid contained in a pressure vessel through at least one nozzle to form a cutting jet. The gas generator of the present invention may be comprised of relatively simple components that generate the pressure required to create a fluid cutting jet. In addition, the gas generator of the present invention may be configured so that it may be reused by reloading the tool with a solid propellant cartridge and refilling the pressure vessel with fluid. The solid propellant may comprise a composite fuel and oxidizer, and may be formed or cast into a tube as known in the art. The propellant may, by way of example only, comprise a Class 1.3 propellant. Exemplary types of suitable propellants for the gas generator include, without limitation, composite solid propellants, double base solid propellants, liquid propellants and pyrotechnic materials. Also, the gas generator may include an actuation device for igniting the solid propellant, as known in the art. A remote, wireless actuation system may be optionally employed.

[0021] Generally, the propellant-powered fluid jet cutting apparatus of the present invention, being self-contained may, in one embodiment, be suitably configured to be lowered into a tubular structural element, either by a drill string or, more preferably, by a wireline or coiled tubing string, as known in the art, to a location within a borehole just above the point where it is believed or has been determined that the tubular structural element is stuck within the borehole. Alternatively, in the case of removal for salvaging, such as casing in an abandoned borehole, the propellant-powered fluid jet cutting apparatus of the present invention may be lowered to a desired depth. Further and optionally, an anchoring mechanism may be used to fix the position of the propellant-powered fluid jet cutting apparatus during use and may be used in conjunction with a centering device for centering the propellant-powered fluid jet cutting apparatus within the tubular structural element to be cut by the propellant-powered fluid jet cutting apparatus.

[0022] In one embodiment of the propellant-powered fluid jet cutting apparatus of the present invention, an electrical signal may be generated and transmitted from a remote location to cause the propellant to ignite within the gas generator. As the propellant bums, the gases that are produced pressurize a pressure vessel containing fluid in communication with the propellant gas generator. The pressure vessel containing fluid may contain a gas as well as a fluid and each may be physically separated from one another by way of a separation element, e.g., a piston or a membrane, so that the gases produced by the gas generator do not contact or mix with the fluid within the pressure vessel or visa versa. In addition, an energy storage device such as a piston or bladder accumulator may be used to store the pressure produced via the gas generator and may be installed on either side of the separation element. Use of such an energy storage device may facilitate prolonged release of pressure and thus propulsive energy for driving the cutting fluid. Attached to the pressure vessel is a nozzle assembly comprising at least one nozzle configured, under suitable supply pressure, to produce a fluid cutting jet for cutting through tubular metal structures. A burst disc may prevent the pressurized fluid from exiting the pressure vessel and passing to the nozzle assembly until a threshold pressure above which causes the burst disc to rupture is reached. In addition, a pressure relief element may be installed between the gas generator and the separation element to prevent the gas generator from over-pressurizing the pressure vessel.

[0023] The nozzle assembly may comprise a plurality of nozzles and, if intended for cutting a tubular structural element, may be configured, sized, and located to rotate as high pressure fluid exits therefrom. Rotation may be desirable to circumferentially equalize the cutting of a tubular structural element. “Equalizing the cutting” as used herein means that any unequal cutting that may occur because of differences in the nozzles or in the pressure distribution within the nozzle assembly may be equalized periodically by exposing the interior surface of the tubular structural element to be cut to all of the nozzles, thereby equalizing the overall cutting process of the tubular structural element. Rotation of the nozzle assembly may be caused by way of a mechanical system, i.e., a gear system, or may be powered by the pressure or flow of the fluid in the pressure vessel or gas escaping from the relief element to drive a rotor, an electric/hydraulic motor, or by way of reactive forces of the high pressure cutting jets. In addition, due to the relatively high reactive forces created by the cutting jets, the nozzles of the nozzle may be located, sized and oriented so as to eliminate unwanted moments on the nozzle assembly. The nozzle assembly may further comprise dynamic seals to accommodate rotation thereof.

[0024] Alternatively, the entire propellant-powered fluid jet cutting apparatus may be rotated by a motor, drill string, or as otherwise known in the art, without independent rotation of the nozzle assembly. However, in the case of a rotating nozzle assembly, it may be advantageous to rotate the entire propellant-powered fluid jet cutting apparatus in the opposite direction as the rotation of the nozzle assembly, so that the rotation of the nozzle assembly with respect to the tubular structural element to be cut may be adjusted. For instance, the nozzle assembly may rotate relatively quickly and by simultaneously rotating the propellant-powered fluid jet cutting apparatus in the opposite direction, the nozzle assembly rotation with respect to the surface to be cut may be slowed. Conversely, rotation of the propellant-powered fluid jet cutting apparatus in the direction of rotation of the nozzle assembly may increase the speed of the cutting jets in relation to the tubular structural element to be cut.

[0025] Alternatively, the nozzle assembly, the nozzles, or both, may be configured to cut a desired area without rotation. Nozzles may be focused at a particular area, or may be positioned to overlap along the circumference of the tubular structural element to be cut. Furthermore, a substantially circumferential fluid cutting jet may be created so that rotation of the nozzle assembly may be unnecessary. Similarly, the nozzle assembly may be configured for cutting a nontubular structural element such as a steel plate, using a series of suitably located nozzles or a drive assembly to move the nozzle assembly in a desired path, or both.

[0026] The nozzle assembly may also comprise one or more nozzles attached to the nozzle assembly and movable with respect thereto so that different diameters of tubular structural elements may be cut. A movable nozzle may be rigidly attached and adjustable in position and orientation as known in the art, i.e., bolts, fixtures, pins, etc. A movable nozzle may be hingedly or pivotably attached to the nozzle assembly so that during rotation of the nozzle assembly, the nozzle is biased radially outward until the nozzle, a roller, or another contact element touches the inner diameter of the tubular structural element to be cut. Thus, it may be advantageous to employ a movable nozzle to achieve a desired standoff or distance between the nozzle exit and the tubular structural element to be cut.

[0027] Moreover, the propellant-powered fluid jet cutting apparatus of the present invention may include a cutting enhancement material as part of the fluid cutting jet produced by a nozzle in the nozzle assembly to further enhance the cutting capability of the fluid cutting jet. The cutting enhancement material may comprise an abrasive such as glass, garnet, silica sand, cast iron, alumina, silicon carbide or other suitable medium. Further, it is contemplated by the present invention to add chemicals to the pressure vessel fluid to enhance the cutting capability of a fluid cutting jet as it exits a nozzle of the nozzle assembly in communication with the pressure vessel. Therefore, the cutting enhancement material may comprise either a solid or fluid and may be soluble or insoluble with the pressure vessel fluid with which it is mixed. It may be advantageous to hold the cutting enhancement material in solution so that the cutting enhancement material will not segregate from the fluid. In addition, it may be advantageous to add the cutting enhancement material to the high pressure fluid within the pressure vessel near a nozzle exit forming a cutting jet, to reduce wear or erosion of the internal fluid passageways of the fluid jet cutter.

[0028] As a further consideration, it may be desired to cut only a certain radial amount or thickness of tubing or pipe, thereby preserving the materials surrounding the tubing or pipe intended to be cut by the propellant-powered fluid jet cutting apparatus. Similarly, for cutting nontubular structural elements, a limited cutting range may be desirable to minimize damage to components or materials “behind” the wall of the structural element. Therefore, the propellant-powered fluid jet cutting apparatus of the present invention may be configured to have a selected, effective cutting range by configuring the cutting jets with limited velocity and/or duration. In addition, it may be advantageous to orient and direct fluid cutting jets so that they intersect proximate an outer diameter of the tubular structural element to be cut, or proximate an outermost periphery that is desired to be cut. Because cutting jets have limited effective cutting range, depending on their coherency, such an arrangement may inhibit the cutting jets from cutting beyond their intersection position, because interference of the intersecting jets may reduce or eliminate their effectiveness as cutting implements.

[0029] As a further application, it is within the scope of the present invention that forming apertures or “windows” in a structural element may be accomplished with the propellant-powered fluid jet cutting apparatus. The present invention further contemplates that the propellant-powered fluid jet cutting apparatus may be used to create so-called “perforations” through a casing disposed within a borehole and, optionally, into the surrounding formation in order to initiate or increase hydrocarbon production from the borehole.

[0030] Features from any of the above mentioned embodiments may be used in combination with one another in accordance with the present invention. In addition, other features and advantages of the present invention will become apparent to those of ordinary skill in the art through consideration of the ensuing description, the accompanying drawings, and the appended claims.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0031] In the drawings, which illustrate what is currently considered to be the best mode for carrying out the invention:

[0032]FIG. 1 is a schematic side cross-sectional view of an embodiment of a propellant-powered fluid jet cutting apparatus of the present invention;

[0033]FIG. 2A is a schematic top view of a nozzle assembly of the present invention;

[0034]FIG. 2B is a schematic side view of the nozzle assembly shown in FIG. 2A;

[0035]FIG. 3A is a schematic top view of a nozzle assembly of the present invention;

[0036]FIG. 3B is a schematic side view of the nozzle assembly shown in FIG. 3A;

[0037]FIG. 4A is a partial cross-sectional schematic side view of a nozzle assembly body of the present invention;

[0038]FIG. 4B is a partial cross-sectional schematic side view of a nozzle assembly body of the present invention;

[0039]FIG. 4C is a partial cross-sectional schematic side view of a nozzle assembly body of the present invention;

[0040]FIG. 5A is a partial cross-sectional schematic side view of a movable nozzle of the present invention;

[0041]FIG. 6 is a schematic side cross-sectional view of another embodiment of a propellant-powered fluid jet cutting apparatus of the present invention;

[0042]FIG. 7 is an enlarged schematic side cross-sectional view of an anchoring mechanism shown in FIG. 6;

[0043]FIG. 8 is a schematic side cross-sectional view of an embodiment of a nozzle assembly of the present invention;

[0044]FIG. 9 is a schematic side cross-sectional view of another embodiment of a nozzle assembly of the present invention; and

[0045]FIG. 10 is a schematic side cross-sectional view of a further embodiment of a propellant-powered fluid jet cutting apparatus of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0046]FIG. 1 shows a schematic side cross sectional view of the propellant-powered fluid jet cutting apparatus 10 of the present invention. Propellant-powered fluid jet cutting apparatus 10 includes gas generator 14 in communication with pressure vessel 16, which is hydraulically connected to nozzle assembly 34. More specifically, gas generator 14 supplies gas to at least a small gas-containing volume 18 of pressure vessel 16, thus increasing the pressure in the gas-containing volume 18. Use of a gas-containing volume is desirable to accommodate gas suddenly developed by gas generator 14 upon initiation, accommodating the necessary time involved in transferring energy to fluid-containing volume 20 within pressure vessel 16 and alleviating the risk of bursting pressure vessel 16 from overpressuring in excess of its designed pressure rating plus safety margin. As gas generator 14 creates gases and increases the pressure within the gas-containing volume 18, separation element 26 transmits the force on the gas-facing surface 27 thereof through the separation element 26 to the liquid-facing surface 29 of separation element 26 to increase the pressure within fluid-containing volume 20. Upon reaching a sufficient pressure within the fluid-containing volume 20, burst disc 31 ruptures to allow fluid to flow from the fluid-containing volume 20 of pressure vessel 16 into the nozzle assembly 34 and out of nozzles 36. Pressure relief element 22 allows gas to escape from pressure vessel 16 in order to limit the amount of pressure within pressure vessel 16 and may be sized and configured according to anticipated gas generation rate and volume of gas generator 14 and total fluid flow rate of nozzle assembly 34. Of course, the pressure at which pressure relief element 22 allows gas to escape from pressure vessel 16 must be higher than the pressure at which the burst disc 31 ruptures, otherwise the burst disc 31 may not rupture and the gas generated via the gas generator 14 may simply vent through the pressure relief element 22. Alternatives to burst disc 31 may include a diaphragm or a check valve. Fill port 24 extends from pressure vessel 16 and is in communication with fluid-containing volume 20 so that fluid-containing volume 20 may be refilled with a suitable fluid after operation of fluid jet cutter 10 causes the fluid within containing volume 20 to be expelled from the pressure vessel 16.

[0047] Nozzle assembly 34 may include one or more nozzles 36 that may be configured and sized to cut an intended area of a tubular structural element 40 in which propellant-powered fluid jet cutting apparatus 10 is deployed. Although the present invention has been described as cutting the entire circumference of a tubular structural element 40 for removal, the present invention may be used to cut only a particular area of the tubular structural element 40. For instance, cutting windows within casing elements in a borehole may be accomplished. It may be possible to configure and size nozzles 36 so that particular areas of the tubular structural element are severed relatively more quickly than other areas of the tubular structural element. Such a configuration may be suited for tubular structural elements having varying compositions or wall thicknesses, so that relatively increased severing capability may correspond to the configuration of the tubular structural element to be cut.

[0048] Nozzle assembly 34 may be rotatably attached to stem 32 extending from pressure vessel 16 via bearings 28 and 30. Bearings 28 and 30 are shown schematically above and below nozzle assembly 34, but may, for example, be pressed into the body of nozzle assembly 34 at each bearing 28/30 outer diameter and also installed onto the stem 34 at each bearing 28/30 inner diameter, as known in the art. Stem 32 includes one or more fluid ports (not shown) for communicating fluid from the fluid-containing volume 20 of pressure vessel 16 into the nozzle assembly 34 and ultimately through nozzles 36. Nozzle assembly 34 may include a rotating seal (not shown) that allows rotation of nozzle assembly 34 while providing a dynamic fluid seal between the stem and the nozzle assembly 34. An electric motor (not shown) may be operably coupled to stem 32 as well as nozzle assembly 34, in order to rotate nozzle assembly 34 about longitudinal axis 15 of propellant-powered fluid jet cutting apparatus 10 with respect to stem 32 during operation of propellant-powered fluid jet cutting apparatus 10.

[0049] During operation of propellant-powered fluid jet cutting apparatus 10, a number of factors may affect the cutting ability of propellant-powered fluid jet cutting apparatus 10. For instance, the amount of standoff 37 between a nozzle 36 and the tubular structural element 40 to be cut, the thickness 41 of tubular structural element 40, the pressure that the pressure relief element 22 may be configured and sized to maintain, the configuration and size of the nozzle assembly 34 and nozzles 36, the rotational speed of the nozzle assembly 34, as well as the fluid contained within the fluid-containing volume 20 of pressure vessel 16 may affect the cutting capability of propellant-powered fluid jet cutting apparatus 10.

[0050] Further, in operating propellant-powered fluid jet cutting apparatus 10, it may be desirable to center propellant-powered fluid jet cutting apparatus 10 within the tubular structural element 40 so that standoff 37 may be substantially constant around the circumference of propellant-powered fluid jet cutting apparatus 10, or in other words, propellant-powered fluid jet cutting apparatus 10 may be centered within tubular structural element 40. Inflatable packers, or other centering or anchoring devices such as circumferentially placed bow springs, may be disposed within tubular structural element 40 above, below, and/or integral to propellant-powered fluid jet cutting apparatus 10 in order to center propellant-powered fluid jet cutting apparatus 10 within tubular structural element 40. Failure to center propellant-powered fluid jet cutting apparatus 10 within tubular structural element 40 may result in the cutting of tubular structural element 40 being circumferentially uneven. Circumferentially uneven cutting may not be desirable because the jets extending from nozzles 36 may exit the outer radial surface of tubular structural element 40 intended to be cut and may begin to cut another tubular structural element which may not be intended for severing, or may damage the formation behind the tubular structural element being cut.

[0051] As shown in FIG. 1, tubular structural element 40 may be stuck within borehole 50 at annular area 51, where the formation 50 may engage with tubular structural element 40 in an interference fit therewith, thus affixing the tubular structural element 40 within the borehole. As discussed above, propellant-powered fluid jet cutting apparatus 10 may be radially disposed within tubular structural element 40 and may be preferably substantially centered within tubular structural element 40 during severing of the tubular structural element 40. In addition, propellant-powered fluid jet cutting apparatus 10 may be disposed longitudinally above annular area 51 so that cutting of tubular structural element 40 effected by the nozzle assembly 34 will occur above annular area 51 as well. Therefore, after tubular structural element 40 may be severed by the jets exiting nozzle assembly 34 and nozzles 36 thereof, the section of tubular structural element 40 vertically above area 51 may be removable from the formation 50.

[0052] Turning to FIGS. 2A and 2B, each is a schematic representation, and therefore may not be construed to limit the present invention. For instance, bearing 28 and bearing 30 are represented schematically to illustrate that the nozzle assembly body 35 may be rotationally decoupled from and may rotate with respect to stem 32. More specifically, in a two-race ball bearing, comprising two bearing races separated by balls therebetween, one race may be affixed to the nozzle assembly body 35 and the other race may be affixed to the stem 32. Often, bearing races may be press fit within or shrink fit onto a recess or shaft, respectively, depending on the bearing race to be affixed, but may be affixed to another component via threaded connectors, welding, or as otherwise known in the art. Further, nozzles 36 of nozzle assembly 34 are shown to extend radially outwardly from nozzle assembly body 35, but may be disposed so that nozzles 36 do not extend past the outermost radial extent of the nozzle assembly body 35, as shown in FIGS. 4A and 4B. Such a configuration may protect the nozzles 36 during use.

[0053] As shown in FIG. 2A, nozzle assembly 34 may include a plurality of nozzles 36. Nozzle assembly 34, as shown in FIGS. 2A and 2B, includes six nozzles 36 disposed about the circumference of a nozzle assembly body 35. Nozzles 36 may be arranged to be equally spaced about the circumference of the nozzle assembly body 35. Such a symmetric arrangement may reduce or substantially eliminate net forces and moments generated by the fluid cutting jets, due to the acceleration of the fluid as it exits the nozzles 36. More specifically, each jet from each nozzle 36 creates a reaction force, analogous to the reaction force created from fluid exiting a garden hose or fire hose that may be transferred to each nozzle 36 and therethrough to the nozzle assembly 34. In the configuration shown in FIGS. 2A and 2B, each nozzle 36 may be substantially diametrically opposed by another nozzle 36 positioned at substantially 180° from the first nozzle, so that each reaction forces generated by the two opposing fluid cutting jets substantially cancel one another. This may aid in prolonging bearing longevity by reducing forces thereon and facilitate rotation thereof. In addition, each nozzle 36 may be configured so that its reaction force passes through the rotational axis of the nozzle assembly 34. Since the reaction force of a fluid cutting jet may be exerted in the opposite direction of the fluid cutting jet, the fluid cutting jets depicted in FIGS. 2A and 2B by arrows extending from nozzles 36, it may be seen that the nozzles 36 may be positioned and oriented so that the reaction forces of each fluid cutting jet pass through the center of rotation 5 of the nozzle assembly 34. As such, the nozzles 36 may be oriented and positioned so that substantially no moment may be produced via the fluid cutting jets about the nozzle assembly 34 or nozzle assembly body 35.

[0054] Accordingly, the nozzle assembly 34 in a configuration shown in FIGS. 2A and 2B may not, during operation, produce a sufficient net moment to cause the nozzle assembly 34 to rotate with respect to stem 32 as well as longitudinal axis 15. Therefore, a moment may be supplied to the nozzle assembly 34, and more specifically, to the nozzle assembly body 35 so that the nozzles 36 are caused to rotate about the longitudinal axis 15 of the propellant-powered fluid jet cutting apparatus 10. For instance, a motor may be used to rotate the nozzle assembly 34. More specifically, a motor powered by electricity supplied from the surface of the formation or via batteries or other storage devices may be used to rotate the nozzle assembly 34. Similarly, hydraulic motors, turbines, or other rotation devices may be employed, and may be powered via the gas generator 14 used to power the propellant-powered fluid jet cutting apparatus 10, or may be powered as otherwise known in the art.

[0055] Alternatively, the reactive force generated by the fluid as it exits a nozzle 36 may be oriented and positioned to rotate the nozzle assembly body 35 about the stem 32 and longitudinal axis 15. FIGS. 3A and 3B illustrate, schematically, a nozzle assembly 34 with nozzles 36 that are oriented so that a moment may be generated on the nozzle assembly body 35. As in FIGS. 2A and 2B, bearing 28 and bearing 30 are represented schematically to illustrate that the nozzle assembly body 35 may be rotationally decoupled from and may rotate with respect to stem 32. However, each nozzle 36 may be oriented so that the reaction force may create a moment about the center of rotation 5 of the nozzle assembly 34. As shown in FIG. 3A, the line 7 along which the reaction force acts may be positioned at a perpendicular distance d from the center of rotation 5 of nozzle assembly 34. Therefore, the counter-clockwise moment generated by way of one nozzle 36 equals the product of the reaction force of one nozzle 36 and distance “d.” The cumulative moment acting on the nozzle assembly 34 may equal the summation of the products of the reaction forces and the perpendicular distances from the center of rotation 5 of the nozzle assembly 34.

[0056] Accordingly, the orientation and position of the nozzles 36 of the nozzle assembly 34 may be configured to produce a desired moment during operation of a propellant-powered fluid jet cutting apparatus. Also, since the size of the exit orifice of a nozzle 36 may, to an extent, determine the acceleration of a fluid and thereby the reaction force produced via the nozzle 36, the size of the exit orifice of a nozzle 36 may be adjusted to produce a desired moment during operation of a propellant-powered fluid jet cutting apparatus. However, orienting a nozzle so that a moment may be created via the jet exiting therefrom may affect the ability of the fluid cutting jet to cut a tubular structural element. Therefore, the present invention contemplates that particular nozzles may be oriented, sized, and positioned in order to create a moment that may cause the nozzle assembly 34 to rotate, while other nozzles are sized, configured, and positioned to cut a tubular structural element. Of course, if a moment-producing nozzle may be configured to adequately cut a tubular structural element, then such a combination may be unnecessary.

[0057]FIG. 4A shows a partial cross-sectional schematic view of a nozzle assembly body 35 including a nozzle 36 and a fluid aperture 39 for communicating fluid therethrough to create a fluid cutting jet exiting the nozzle 36 in a direction perpendicular to the longitudinal axis 56 of nozzle assembly body 35. Nozzle 36 may be formed from tungsten carbide, silicon carbide, ceramic, or may be formed of steel with a ceramic coating. One particularly suitable steel, by way of example only is so-called “Maraging” steel, as described in approved for public release Military Specification MIL-S-46850D of Mar. 21, 1991, entitled STEEL: BAR, PLATE, SHEET, STRIP, FORGING, AND EXTRUSIONS, 18 PERCENT NICKEL ALLOY, MARAGING, 200 KSI, 250 KSI, 300 KSI, AND 350 KSI, HIGH QUALITY. The nozzle orifice should be formed or lined with a material to resist wear thereof and may include a jewel having an aperture therethrough, as known in the art, typically of ruby, sapphire, diamond or other superabrasive configured to resist wear or erosion as the fluid exits therefrom. Alternatively, a jewel surface coating or surface treatment may be employed to form at least a portion of the nozzle 36. Nozzle 36 may be threaded into the nozzle assembly body 35, or otherwise affixed therein and may preferably be replaceable. In addition, it may be preferable to introduce abrasives proximate to the fluid cutting jet exiting the nozzle to prevent unwanted or excessive wear on the fluid passageways and the nozzle of the propellant-powered fluid jet cutting apparatus. However, in the alternative, abrasives or other additives that enhance the cutting ability of a fluid cutting jet may be introduced into the fluid at any stage within the propellant-powered fluid jet cutting apparatus of the present invention, or prior to placing the fluid within the propellant-powered fluid jet cutting apparatus. For instance, the fluid and a cutting enhancement material may be in solution or held in suspension in the form of a slurry within the propellant-powered fluid jet cutting apparatus of the present invention so that no additional materials are mixed with the fluid as it travels therethrough and exits the nozzle assembly 34.

[0058] As a further consideration, the present invention contemplates tilting a nozzle 36 vertically, as shown in FIG. 4B, so that the jet may not be perpendicular with angle with the longitudinal axis 15 of the nozzle assembly 34. As shown in FIG. 4A, the direction of the jet forms angle θ with respect to reference line 66, line 66 being perpendicular to longitudinal axis 56. The jet created thereby may be directed to cut an annulus of a tubular structural element that may differ in longitudinal position from another nozzle 36 within the same nozzle assembly 34. Such a configuration may be useful for ensuring that the tubular structural element may be severed, or may be useful in cleaning applications, where it may be desired to increase the area affected by fluid cutting jets exiting the nozzles 36. Of course, nozzles 36 may be configured to be substantially diametrically opposed with regard to their vertical reaction forces, so that the vertical reaction force generated by each fluid cutting jet exiting a nozzle is substantially cancelled by the force generated via a substantially diametrically opposed fluid cutting jet exiting another nozzle 36.

[0059] As another contemplation of the present invention, fluid cutting jets exiting nozzles 36 may be positioned and oriented to intersect. Fluid cutting jets that intersect may be advantageous for altering the cutting ability of the jets, particularly for limiting the cutting ability thereof. For instance, it may be advantageous to configure nozzles so that a wide range of materials and material thicknesses may be severed. A fluid cutting jet may possess cutting ability related to its coherency until intersection with another fluid cutting jet, thus reducing coherency and greatly reducing or eliminating cutting ability of each fluid cutting jet. As further shown in FIG. 4C, the intersection location of fluid cutting jets of nozzle 76 and nozzle 77 may be configured to be substantially proximate to the outer radial surface of a tubular structural element 40. Nozzle 77 forms a fluid cutting jet in a direction that forms angle y with reference line 87, reference line 87 being perpendicular to longitudinal axis 56. Similarly, nozzle 76 forms a fluid cutting jet in a direction that forms angle θ with reference line 86, reference line 86 being perpendicular to longitudinal axis 56. During operation, the fluid cutting jets formed via nozzles 77 and 76 exit each nozzle, respectively, and travel radially outwardly until contacting the inner radial surface 43 of tubular structural element 40. FIG. 4C is schematic and therefore the nozzles may be much closer to tubular structural element 40 in actual practice. The fluid cutting jets of nozzle 76 and 77 each cut through tubular structural element 40, and may possess, if unhindered, cutting ability that extends radially beyond the outer radial surface 45 of tubular structural element 40. However, it may be desired to limit the cutting ability of the fluid cutting jets exiting nozzle 76 and 77 by orienting and positioning nozzles 76 and 77 so that the fluid cutting jets exiting therefrom intersect. As shown in FIG. 4C, the fluid cutting jets formed via nozzles 76 and 77 intersect at point 90, substantially corresponding to the radial position of outer radial surface 45 of tubular structural element 40. Such a configuration may prevent fluid cutting jets from cutting materials that are not intended to be cut, such as a casing in which another tubular structural element may be stuck. It may be desired to cause fluid cutting jets to intersect at a position slightly radially outward from the outermost radial surface of the tubular structural element to be cut as a factor of safety to ensure that the entire thickness of the material may be cut.

[0060] Of course, many configurations of intersecting fluid cutting jets are possible, and are contemplated by the present invention. Turning to FIG. 2A, at least two nozzles 36 may be oriented and positioned along the circumference of nozzle assembly body 35 to cause the fluid cutting jets exiting therefrom to intersect at a desired radial position. In addition, multiple nozzles may be oriented and positioned so as to create fluid cutting jets that intersect.

[0061] As an additional nozzle embodiment, FIG. 5A shows a movable nozzle configuration in a partial cross-sectional schematic view. Movable nozzle 92, shaped generally as a multi-diameter piston, includes a movable nozzle passageway 93 for communicating fluid to the nozzle 96, which may be formed from a highly wear resistant material as discussed hereinabove, or include a jewel insert with an aperture therethrough as known in the art. Fluid moving through nozzle passageway 39 travels toward movable nozzle 92. Pressure developed within nozzle passageway 39 acts on surface 95 of movable nozzle 92 forcing the movable nozzle 92 radially outward. Surface 98 of retention element 94 matingly engages surface 97 of movable nozzle 92, thus positioning movable nozzle 92 at its outermost radial position. Of course, sealing elements may be disposed between movable nozzle 92 and nozzle passageway 39, retention element 94 as desired and known in the art to prevent high pressure fluid from escaping therebetween. Movable nozzle passageway 93 communicates fluid therethrough to the nozzle 96 from which the fluid exits, thus forming a fluid cutting jet. Retention element 94 may be threaded into nozzle assembly body 35, or otherwise affixed thereto. Further, retention element 94 may be configured to be replaceable, and may be configured to be adjustable so that the outermost radial position of the movable nozzle 92 may be adjusted. Furthermore, a biasing element (not shown) such as a coil, leaf, belleville or other spring may be disposed between surface 97 of movable nozzle 92 and surface 98 of retention element 94 so as to force the movable nozzle 92 radially inwardly when fluid pressure within nozzle passageway 39 may be less than the force provided by the biasing element. A biasing element (not shown) may be useful in positioning a movable nozzle 92 radially inward so as to prevent damage to the movable nozzle 92 during deployment within a tubular structural element or removal therefrom.

[0062] Although the embodiment of the movable nozzle 92 shown in FIG. 5A is configured as a multi-diameter piston so that pressure developed within the nozzle passageway 39 cause the movable nozzle 92 to be forced radially outwardly, there are many contemplated alternatives. For instance, nozzles may be configured on the ends of flexible high pressure hoses, or attached to nozzle arms that are hingedly attached to the nozzle assembly body so that in either case the nozzles may be displaced radially outwardly and toward the surface of the material to be cut. In such a configuration, if the nozzle assembly rotates, the centrifugal force from the rotation of the nozzle assembly may cause the nozzles to be forced radially outwardly, or the reaction force of a fluid cutting jet may be used to force the nozzles radially outwardly. Further, combinations of pressure, reaction force via fluid flow, or centrifugal force may be used as desired to position a movable nozzle in relation to a material to be cut.

[0063] A movable nozzle may be particularly useful for positioning a fluid cutting jet in relation to material to be cut, so that the fluid cutting jet may be effective for cutting the desired thickness of material. As mentioned hereinabove, a fluid cutting jet's cutting ability may be related to its coherency, which may deteriorate as the distance from the nozzle exit increases. Therefore, it may be advantageous to position the exit of the nozzle immediately proximate to the material to be cut. Conversely, if the fluid cutting jet has cutting ability, in terms of distance from the nozzle exit that may be cut, that exceeds the desired outermost extent of the material to be cut, the nozzle size may be limited so that its effective cutting distance only slightly exceeds or equals the outer extent of the material to be cut.

[0064] In the case that it is desired to position a movable nozzle as closely as possible to the material to be cut, and where the nozzle assembly may rotate, it may be advantageous to include a rolling element (not shown) such as a wheel near the radial tip of the movable nozzle, so that the rolling element contacts the surface of the material to be cut, and thereby positions the nozzle in substantially constant dimensional relation to the surface of the material to be cut and provides ease in rotation of the nozzle along the material to be cut.

[0065]FIG. 6 shows another embodiment of a propellant-powered fluid jet cutting apparatus 110 of the present invention generally depicted as a number of tubular structural elements threadedly attached to one another. An end cap 115, including an eyelet 107 for connecting a wireline thereto, may be threadedly connected to a gas generator 114 formed via a tubular structural element 111 that contains a propellant 117. As noted previously, the propellant may comprise a solid propellant including a composite fuel and oxidizer, and may be formed or cast into a tube as known in the art. The propellant may, by way of example only, comprise a Class 1.3 propellant. Exemplary types of suitable propellants for the gas generator include, without limitation, composite solid propellants, double base solid propellants, liquid propellants and pyrotechnic materials. The total burn time of an initiated propellant may comprise, by way of example only, about 30 seconds to a minute and will, of course be dependent upon the type, volume and shape of the propellant. In addition, the selected propellant should have a self-energizing temperature at or above 400° F. (or above whatever the expected ambient temperature to be encountered, for example downhole, will be) and a flame temperature between about 2000° and about 4000° F. One specific but exemplary suitable propellant is an AN-based composite solid propellant.

[0066] Gas generator 114 may be threadedly connected to an optional anchoring mechanism 170 at threaded joint 121, anchoring mechanism 170 containing movable elements for engaging the surface of the material to be cut, e.g., the inner diameter of a tubular structural element. An igniter or initiator 101 may be disposed at the lower, distal end of tubular structural element 111 of the gas generator 114 or in the upper distal end of the anchoring mechanism 170 for igniting the propellant 117 within the gas generator 114. An igniter location proximate the lower end of propellant 117 is, of course, desirable so that ignition thereof will generate gas immediately in communication with gas-containing volume 118 (see below). Igniter 101 may be configured as a flat wire sized and positioned to produce an electrical arc between the end of the wire and a portion of the anchoring mechanism 170 or the gas generator 114. Alternatively, the igniter 101 may be disposed within propellant 117, and may comprise a small explosive charge, a resistance heater or a percussion primer. A high voltage or low voltage bridge wire initiator may be employed, and one particularly suitable initiator is a semiconductor bridge igniter disclosed in U.S. Pat. No. 4,708,060 to Bickes, Jr. et al. Anchoring mechanism 170 preferably includes a longitudinally extending port 180 for communicating gas generated by the gas generator 114 to the pressure vessel 116 threadedly connected to the anchoring mechanism 170 at threaded joint 123. Pressure vessel 116 may be formed from tubular structural element 113 and may also contain a separation element 126 (depicted by way of example only as a piston) for separating a gas-containing volume 118 from a fluid-containing volume 120 within the pressure vessel 116. Pressure vessel 116 is shown in a condition where the gas generator 114 has not been deployed, so that fluid-containing volume 120 may be relatively large compared to the gas-containing volume 118. Of course, fluid-containing volume 120 may be adjusted prior to assembly of the propellant-powered fluid jet cutting apparatus 110 by positioning the separation element 126 appropriately and filling the fluid-containing volume 120 with fluid. The lower end of tubular structural element 113 forming pressure vessel 116 may be threadedly attached to nozzle assembly 134 at threaded joint 125.

[0067] It is also contemplated, to simplify construction of a propellant-powered fluid jet cutting apparatus such as apparatus 110, that a remote, wireless igniter or initiator assembly including one of the foregoing types of igniters or initiators 101 be employed. As previously noted, since it is desirable for propellant 117, if a solid propellant to end-burn the propellant grain from the bottom of propellant 117 upwardly, use of a remote, wireless and disposable radio frequency receiver 102 to actuate igniter or initiator 101 enables fabrication of the gas generator 114 without the need for running wires internally or externally. Thus, a simple battery-powered receiver with, if necessary an enhanced power source such as a chargeable capacitor for actuating igniter or initiator 101, may be disposed adjacent and operably coupled with igniter or initiator 101 and a cooperating radio frequency transmitter 103, which may be powered and actuated with a coded initiation signal for safety through a wire line, or which may be self-powered and be actuated through a suitable pressure transducer-type receiver by a coded mud-pulse signal through drilling fluid in the bore hole, to transmit a firing signal to igniter or initiator 101. The transmitter 103 is desirably reusable, although this is not a requirement.

[0068] Moving to FIG. 7, the anchoring mechanism 170 shown in FIG. 6 is depicted in greater detail. Anchoring mechanism 170 includes an upper threaded connection 182 and a lower threaded connection 184, as known in the art, that may be used to connect to a gas generator and pressure vessel as shown in FIG. 6. Port 180 extends longitudinally through the body 183 of anchoring mechanism 170 and, when threadedly connected to gas generator 114 and pressure vessel 116, may allow gas produced via the gas generator 114 to communicate with the pressure vessel 116 therethrough. Further, a pressure relief element 181 may optionally be included within anchoring mechanism 170 and in communication with port 180 to relieve excess pressure generated by way of the gas generator 114. It is contemplated that gas pressure employed for operation of the present invention may be generally in a range of about 30,000 psi and up, with the desired pressure being attributable to the characteristics and thickness of the material to be cut. For example, 50,000 psi may be selected as a maximum selected operating pressure . In addition, anchoring mechanism 170 includes pistons 172 and 174, each including sealing elements 173 and 175, respectively, for sealing the piston to the body 183 of the anchoring mechanism 170, the radially inward end of each of the pistons 172 and 174 being in communication with port 180. Thus, during operation, as high pressure gas from gas generator 114 fills port 180, pistons 172 and 174 are forced radially outward against respective retention elements 176 and 178. Of course, additional pistons such as 172 and 174 may be disposed to extend radially from anchoring mechanism 170 at different circumferential locations to better retain and center apparatus 110 within a borehole. Retention elements 176 and 178 may be affixed respectively to the body 183 of anchoring mechanism 170 by way of threaded connectors 186 and 188 as shown in FIG. 7, or as otherwise known in the art. Retention elements 176 and 178 may be configured to bend as pistons 172 and 174 may be forced radially outward so that the lower end of each retention element 176 and 178 may be forced radially outward and may engage the inner surface of a tubular structural element intended to be severed by the propellant-powered fluid jet cutting apparatus 110 of the present invention. Thus, the anchoring mechanism 170 may be used to temporarily affix a propellant-powered fluid jet cutting apparatus 110 within a tubular structural element intended to be severed thereby. In addition, retention elements 176 and 178 may bias associated pistons 172 and 174 radially inward as pressure within port 180 decreases below the pressure sufficient to cause the retention elements 176 and 178 to engage the surface of a tubular structural element intended to be severed. In addition, the retention elements 176 and 178 may serve to protect the sealing elements 173 and 175 from encountering debris when the anchoring mechanism 170 may not be in use by covering the outer radial surface of the pistons 172 and 174 as shown in FIG. 7.

[0069] Of course, many alternatives exist for providing an anchoring mechanism and are contemplated by the present invention. For instance, the anchoring mechanism may include one or more multi-diameter pistons that may be displaced radially outwardly so that the piston contacts the inner diameter of the tubular structural element intended to be severed when pressure within port 180 forces the piston radially outward. The pistons may be configured so that a portion of the piston may matingly engage the inner surface of the body of the anchoring mechanism to prevent further outward radial movement, similar to the multi-diameter piston as shown in FIG. 5A. Further, a biasing element, e.g., a spring, may be configured, sized, and positioned to return the piston radially inward when the pressure within port 180 may not be sufficient to maintain the piston's radial position. Furthermore, tapered, mechanically set elements such as packer-type slips, inflatable elements, or other mechanisms known in the art may be used to anchor and/or position a propellant-powered fluid jet cutting apparatus of the present invention. It is contemplated that an anchoring mechanism that contacts the wall of the tubular element throughout an entire inner periphery thereof may be employed for anchoring and centering apparatus 110.

[0070] Turning to FIG. 8, the nozzle assembly 134 shown in FIG. 6 is depicted in detail. The nozzle assembly 134 includes a nozzle housing 152 threadedly affixed to a nozzle retainer 156, the nozzle retainer 156 being also threadedly affixed to nozzle end cap 154. Burst disc 131 may be affixed to the upper longitudinal end of nozzle housing 152, thus preventing flow therethrough until a sufficient pressure may be supplied to rupture burst disc 131. Of course, valves, pressure actuated valves, electric valves, or other flow control devices may be used in place of or in combination with burst disc 131. Nozzle retainer 156 may be threadedly affixed to nozzle end cap 154 by way of inner threaded surface 155 as well as nozzle housing 152 by way of outer threaded surface 157, the nozzle retainer 156 having one or more passageways 159 for allowing fluid to pass therethrough. During operation, fluid may pass through ruptured burst disc 131, through the upper longitudinal area of nozzle housing 152, through one or more passageways 159, and then through area 163 formed between the nozzle housing 152 and the nozzle end cap 154, and then exiting circumferentially between a nozzle ring 158 affixed to nozzle housing 152 and a nozzle ring 160 affixed to nozzle end cap 154. Nozzle ring 158 and nozzle ring 160 may be separated by, for example, about 0.005 to about 0.015 inches and may also include a jeweled (diamond, sapphire, etc.) or otherwise wear/erosion resistant surface for producing a sufficiently coherent fluid cutting jet for severing a tubular structural element. In addition, it may be necessary to provide spacers (not shown) or other spacing elements (not shown) for adjusting and/or maintaining the relative positions of nozzle ring 158 and nozzle ring 160 during use. Spacing elements (not shown) may be positioned between nozzle ring 158 and nozzle ring 160, or alternatively, between nozzle housing 152 and nozzle end cap 154 in order to adjust or maintain the position of nozzle ring 158 with respect to nozzle ring 160 to adjust the clearance therebetween. Thus, nozzle assembly 134 may produce a substantially circumferential fluid cutting jet for cutting a tubular structural element. A circumferential fluid cutting jet may be advantageous in that a rotating nozzle assembly may not be required if the inner diameter of a tubular structural element may be severed by way of a substantially circumferential fluid cutting jet.

[0071]FIG. 9 shows a nozzle assembly 134 for providing two substantially circumferential jets for severing tubular structural elements. Nozzle assembly 134 includes nozzle housing 152 threadedly affixed to nozzle retainer 156, nozzle retainer 156 also being threadedly affixed to nozzle stem 161 and nozzle stem 161 being also threadedly affixed to nozzle end cap 154. Nozzle assembly 134 may include a burst disc 131 affixed to the upper longitudinal end of nozzle housing 152, thus preventing flow therethrough until a sufficient pressure may be supplied to rupture burst disc 131. During operation, fluid may pass through ruptured burst disc 131, through the upper longitudinal area of nozzle housing 152, through one or more passageways 159, and then through annular area 163 formed between the nozzle housing 152 and the nozzle stem 161, and may exit nozzle assembly 134 circumferentially between a nozzle ring 158 affixed to nozzle housing 152 and a nozzle ring 160 affixed to nozzle stem 161. During operation, fluid may also pass through passageway 164, through the area 153 formed between nozzle stem 161 and nozzle end cap 154, and may exit between nozzle ring 168 affixed to nozzle stem 161 and nozzle ring 169 affixed to nozzle end cap 154. Nozzle rings 158 and 160 as well as nozzle rings 168 and 169 may be separated by about 0.005 inches and may also include a jeweled or otherwise wear/erosion resistant surface for producing a sufficiently coherent fluid cutting jet for severing a tubular structural element. Thus, the nozzle assembly 134 of the present invention may be configured to produce more than one substantially circumferential fluid cutting jet.

[0072] It is also contemplated by the present invention that substantially circumferential fluid cutting jets may be configured to intersect. Referring back to FIG. 4C, nozzle assembly 134 shown in FIG. 9 may be configured so that the substantially circumferential fluid cutting jet exiting between nozzle ring 158 and nozzle ring 160 may intersect with the fluid cutting jet exiting between nozzle ring 168 and nozzle ring 169, similar to the intersection at point 90 as shown in FIG. 4C, except that the intersection of substantially circumferential fluid cutting jets may generate a substantially circumferential intersection. Further, during operation, the substantially circumferential fluid cutting jet exiting between nozzle ring 158 and nozzle ring 160 and the fluid cutting jet exiting between nozzle ring 168 and nozzle ring 169 may travel radially outwardly until contacting the inner radial surface of a tubular structural element. Similar to FIG. 4C, the substantially circumferential fluid cutting jet exiting between nozzle ring 158 and nozzle ring 160 and the substantially circumferential fluid cutting jet exiting between nozzle ring 168 and nozzle ring 169 may be configured to intersect circumferentially at substantially the radial position of outer radial surface of the tubular structural element to be severed. Such a configuration may prevent substantially circumferential fluid cutting jets from cutting materials that are not intended to be cut, such as a casing in which another tubular structural element may be stuck. It may be desired to cause substantially circumferential fluid cutting jets to intersect at a position slightly radially outward from the outermost radial surface of the tubular structural element to be cut as a factor of safety to ensure that the entire thickness of the material is cut.

[0073] Turning to FIG. 10, another embodiment of the propellant-powered fluid jet cutting apparatus 310 of the present invention is shown. End cap 312 may be threadedly connected to tubular structural element 311, tubular structural element 311 forming both gas generator 314 as well as pressure vessel 316. Separation element 326 separates gas-containing volume 318 from fluid-containing volume 320. In addition, pressure relief element 322 allows for gas within gas-containing volume 318 to escape in order to limit the magnitude of pressure within pressure vessel 316 and may be sized and configured according to anticipated gas generation of gas generator 314 and total fluid flow rate of nozzle assembly 334. Separation element 326 is shown as an annular piston, which allows for storage element 313 to be installed central to the tubular structural element 311 so that separation element 326 may move along the outer circumference of storage element 313. Of course, separation element 326 may include on its inner and outer circumferences sealing elements (not shown) for sealing the pressure generated via gas generator 314 within the gas-containing volume 318 from the fluid-containing volume 320. Storage element 313 may include at least one passageway 308 in fluid communication with fluid-containing volume 320, and may be used to store an abrasive for mixing with the fluid contained within fluid-containing volume 320. Alternatively, storage element 313 may be configured as an energy storage device, e.g., an accumulator, and may also contain fluid that may be used to create a fluid cutting jet. Adaptor 315 may be configured to be threadedly affixed to tubular structural element 311 as well as nozzle assembly 334, and, in addition, may provide a threaded connection to storage element 313, as shown in FIG. 10. Nozzle assembly 334 includes a nozzle housing 352 threadedly affixed to a nozzle retainer 356 wherein the nozzle retainer 356 may also be threadedly affixed to nozzle end cap 354. A burst disc 331 may be affixed to the upper longitudinal end of nozzle housing 352, thus preventing flow therethrough until a sufficient pressure may be supplied to rupture burst disc 331. Nozzle retainer 356 may be threadedly affixed to nozzle end cap 354 as well as nozzle housing 352, the nozzle retainer 356 having one or more passageway 359 for allowing fluid to pass therethrough. During operation, fluid may pass through ruptured burst disc 331, through the nozzle housing 352, through one or more passageway 359, and then through area 363 formed between the nozzle housing 352 and the nozzle end cap 354, and then exiting between a nozzle ring 358 affixed to nozzle housing 352 and a nozzle ring 360 affixed to nozzle end cap 354. Nozzle ring 358 and nozzle ring 360 may be separated, by spacers (not shown) or otherwise, by about 0.005 inches and may also include a jeweled or otherwise wear/erosion resistant surface for producing a sufficiently coherent fluid cutting jet for severing a tubular structural element.

[0074] As may be appreciated from the foregoing description, the present invention may be used to cut wall thicknesses in excess of one inch in thickness using a high pressure fluid cutting jet. The nozzles of the fluid jet cutting apparatus of the present invention may be used to accelerate, for example, a small beam of water to a velocity of Mach 2 plus, producing a finely controlled, clean cut with little or no burr at the periphery thereof and no heat-affected zone of the material of the tubular structural element. The self-contained nature of the fluid jet cutting apparatus of the present invention facilitates deployment in deep bore holes at remote locations, as does its reusable nature. Specifically, by refilling the pressure vessel with fluid and inserting a new propellant cartridge in the gas generator, the apparatus may be quickly and easily readied for reuse. Further, as the nozzle assembly may be easily replaced with one of a different lateral extent for cutting a tubular structural element of a different bore diameter, one apparatus with several nozzle assemblies may be used to sever a wide variety of sizes of tubular structural elements.

[0075] The present invention also has wide applicability to a number of non-downhole situations. Further, the compact and robust nature of the apparatus of the present invention as well as its self-contained and self-powered design, renders it suitable for use in remote and difficult to access locations such as mine shafts, subsea applications, demolition applications including without limitation military applications, and others. Of course, the apparatus and the configuration, location and arrangement of the nozzle or nozzles may be custom-tailored to cut, for example, a substantially planar sheet of material, a wall of material, a rectangular or other cross-sectional shaped hollow structural element, as well as windows, slots and other apertures as desired and to cut through solid (non-hollow) structural element. The apparatus of the present invention may also be configured for cutting through chamber, vessel or other compartment walls from the interior or exterior thereof. As noted previously, the apparatus of the present invention, and specifically the nozzle or nozzles, may be associated with a drive mechanism to propel and guide the size and shape of a desired cut. A variety of shapes and sizes of nozzle orifices, as well as orientations thereof, including cooperative orientations, are also contemplated as within the scope of the present invention. As used herein, the term “structural element” is one of convenience, and not of limitation. Accordingly, any material to be cut, whether forming a portion of a “structure” per se or otherwise, is encompassed by the term.

[0076] As may also be seen from the foregoing description, many variations and configurations of gas generators, pressure vessels, separation elements, nozzle assemblies, nozzles, and other propellant-powered fluid jet cutting apparatus components may be possible. Therefore, although the foregoing description contains many specifics, these should not be construed as limiting the scope of the present invention, but merely as providing illustrations of some exemplary embodiments. Similarly, other embodiments of the invention may be devised which do not depart from the spirit or scope of the present invention. Features from different embodiments may be employed in combination with one another. The scope of the invention is, therefore, indicated and limited only by the appended claims and their legal equivalents, rather than by the foregoing description. All additions, deletions, and modifications to the invention, as disclosed herein, which fall within the meaning and scope of the claims are to be embraced thereby. 

What is claimed is:
 1. An apparatus for severing a structural element, comprising: a gas generator in communication with a pressure vessel and comprising a combustible propellant formulated, upon initiation, to supply pressurized gas to the pressure vessel; a fluid within the pressure vessel; and a nozzle assembly in communication with the pressure vessel, the nozzle assembly including at least one nozzle configured for producing a fluid cutting jet.
 2. The apparatus of claim 1, wherein the fluid includes an additive selected from the group consisting of glass, garnet, silica sand, cast iron, alumina, and silicon carbide.
 3. The apparatus of claim 1, further comprising a pressure relief element for releasing gas from the pressure vessel when pressure therein substantially exceeds a preselected pressure magnitude.
 4. The apparatus of claim 3, wherein the pressure relief element is configured and sized to release gas from the pressure vessel when the pressure therein exceeds 50,000 psi.
 5. The apparatus of claim 3, wherein the pressure relief element is configured and sized to release a gas flow of about an excess of the gas generator gas volume production rate over a total fluid volume flow rate of the at least one nozzle at a selected pressure.
 6. The apparatus of claim 5, wherein the selected pressure is the preselected pressure magnitude.
 7. The apparatus of claim 1, wherein the at least one nozzle comprises a plurality of nozzles.
 8. The apparatus of claim 7, wherein at least two nozzles of the plurality of nozzles are configured, sized, and located to create fluid cutting jets that intersect at a selected location exterior to the apparatus.
 9. The apparatus of claim 8, wherein the selected location comprises a location proximate at least a portion of the outer periphery of the structural element to be severed.
 10. The apparatus of claim 1, wherein the at least one nozzle is configured, sized, and located to produce a substantially circumferential fluid cutting jet.
 11. The apparatus of claim 10, wherein the at least one nozzle configured, sized, and located to produce a substantially circumferential fluid cutting jet comprises a plurality of nozzles, each configured, sized, and located to produce a substantially circumferential fluid cutting jet.
 12. The apparatus of claim 11, wherein at least two nozzles of the plurality of nozzles, each configured, sized, and located to produce a substantially circumferential fluid cutting jet are configured, sized, and located to create substantially circumferential fluid cutting jets that intersect at a selected location exterior to the apparatus.
 13. The apparatus of claim 12, wherein the selected location comprises a region proximate at least a portion of an outer periphery of the structural element to be severed.
 14. The apparatus of claim 1, wherein the nozzle assembly is configured to be rotatable about its longitudinal axis.
 15. The apparatus of claim 14, wherein the at least one nozzle comprises a plurality of nozzles.
 16. The apparatus of claim 15, wherein at least two nozzles of the plurality of nozzles are configured, sized, and located to create fluid cutting jets that intersect at a selected location exterior to the apparatus.
 17. The apparatus of claim 16, wherein the at least two nozzles create fluid cutting jets that intersect proximate at least a portion of the outer periphery of the structural element to be severed.
 18. The apparatus of claim 14, wherein the at least one nozzle is configured to produce a fluid cutting jet that creates a reaction force that causes a rotational moment about the longitudinal axis of the nozzle assembly.
 19. The apparatus of claim 1, wherein the at least one nozzle comprises a movable nozzle.
 20. The apparatus of claim 19, wherein the at least one movable nozzle comprises a plurality of movable nozzles.
 21. The apparatus of claim 20, wherein at least two movable nozzles of the plurality of movable nozzles are configured, sized, and located to create fluid cutting jets that intersect at a selected location exterior to the apparatus.
 22. The apparatus of claim 21, wherein the selected location comprises a location proximate at least a portion of an outer periphery of the structural element to be severed.
 23. The apparatus of claim 1, further comprising an anchoring mechanism for preventing motion in at least one degree of freedom of the at least one nozzle with respect to a bore of the structural element to be severed.
 24. The apparatus of claim 23, wherein the anchoring mechanism for preventing motion in at least one degree of freedom of the at least one nozzle is configured, sized, and positioned to substantially align a longitudinal axis of the nozzle assembly with a longitudinal axis of the bore of the material to be severed.
 25. The apparatus of claim 24, wherein the nozzle assembly is configured to be rotatable about its longitudinal axis.
 26. The apparatus of claim 24, wherein the at least one nozzle is configured, sized, and located to produce a substantially circumferential fluid cutting jet.
 27. The apparatus of claim 1, further comprising an energy storage device in communication with the pressure vessel.
 28. The apparatus of claim 1, further comprising a separation element defining a gas-containing volume and a fluid-containing volume associated with the pressure vessel.
 29. The apparatus of claim 28, wherein the separation element comprises a membrane.
 30. The apparatus of claim 28, wherein the separation element comprises a piston.
 31. The apparatus of claim 30, wherein the piston comprises an annular piston.
 32. The apparatus of claim 1, further including an initiator for the combustible propellant, located in proximity thereto.
 33. The apparatus of claim 32, further including a radio frequency receiver operably coupled to the initiator and a radiofrequency transmitter located remotely from the radio frequency transmitter for providing an initiation signal thereto.
 34. The apparatus of claim 33, wherein the radio frequency transmitter is carried by the apparatus.
 35. The apparatus of claim 34, wherein the radio frequency transmitter is configured to receive a coded firing signal to enable the initiation signal.
 36. A method for severing a structural element, comprising: providing a pressure vessel; disposing a fluid within the pressure vessel; initiating a propellant to combustion; and using gas generated by combustion of the propellant to force the fluid out of the pressure vessel and through at least one nozzle to form at least one fluid cutting jet.
 37. The method of claim 36, further including disposing a fluid including an additive selected from the group consisting of glass, garnet, silica sand, cast iron, alumina, and silicon carbide within the pressure vessel.
 38. The method of claim 36, further comprising releasing gas from the pressure vessel when the pressure therein exceeds a preselected magnitude of pressure.
 39. The method of claim 38, wherein releasing gas from the pressure vessel when the pressure therein exceeds a preselected magnitude of pressure comprises releasing gas from the pressure vessel when the pressure therein exceeds 50,000 psi.
 40. The method of claim 38, wherein releasing gas from the pressure vessel when the pressure therein exceeds a preselected magnitude of pressure comprises releasing gas flow of about an excess of a gas volume production rate over a total fluid volume flow rate of the at least one nozzle at a selected pressure.
 41. The method of claim 40, wherein releasing gas flow of about the excess of the gas generator gas volume production rate over the total fluid volume flow rate of the at least one nozzle at a selected pressure comprises releasing gas flow of about the excess of the gas volume production rate over the total fluid volume flow rate of the at least one nozzle at the preselected magnitude of pressure.
 42. The method of claim 36, wherein the at least one nozzle comprises a plurality of nozzles and the at least one fluid cutting jet comprises a plurality of fluid cutting jets.
 43. The method of claim 42, further comprising orienting at least two of the plurality of fluid cutting jets to intersect at a selected location.
 44. The method of claim 43, further comprising orienting the at least two fluid cutting jets to intersect proximate at least a portion of a side of the structural element opposite origin points of the at least two fluid cutting jets.
 45. The method of claim 36, wherein forming the at least one fluid cutting jet comprises forming a substantially circumferential fluid cutting jet.
 46. The method of claim 36, wherein forming at least one fluid cutting jet comprises forming a plurality of substantially circumferential fluid cutting jets.
 47. The method of claim 46, wherein forming a plurality of substantially circumferential fluid cutting jets comprises orienting at least two substantially circumferential fluid cutting jets to intersect at a selected location.
 48. The method of claim 47, wherein orienting the at least two substantially circumferential fluid cutting jets to intersect at a selected location comprises orienting the at least two substantially circumferential fluid cutting jets to intersect proximate at least a portion of an outer periphery of the structural element from within which the circumferential fluid cutting jets emanate.
 49. The method of claim 36, further including rotating the at least one nozzle about a longitudinal axis of a bore of the structural element.
 50. The method of claim 49, wherein forming at least one fluid cutting jet comprises forming a plurality of fluid cutting jets.
 51. The method of claim 50, further comprising orienting at least two fluid cutting jets of the plurality of fluid cutting jets to intersect at a selected location.
 52. The method of claim 51, further comprising orienting the at least two fluid cutting jets to intersect proximate at least a portion of a side of the structural element opposite origin points of the at least two fluid cutting jets.
 53. The method of claim 49, wherein forming at least one fluid cutting jet comprises orienting the at least one fluid cutting jet to create a reaction force causing a rotational moment about the longitudinal axis of the bore of the structural element.
 54. The method of claim 36, further including moving the at least one fluid cutting jet.
 55. The method of claim 54, wherein moving the at least one fluid cutting jet comprises moving a plurality of fluid cutting jets.
 56. The method of claim 55, wherein forming a plurality of substantially circumferential fluid cutting jets comprises orienting at least two substantially circumferential fluid cutting jets to intersect at a selected location.
 57. The method of claim 56, wherein orienting the at least two substantially circumferential fluid cutting jets to intersect at a selected location comprises orienting the at least two substantially circumferential fluid cutting jets to intersect proximate at least a portion of an outer periphery of the structural element from within which the circumferential fluid cutting jets emanate.
 58. The method of claim 36, further comprising anchoring the at least one nozzle in at least one degree of freedom with respect to a bore of the structural element.
 59. The method of claim 58, wherein anchoring the at least one nozzle in at least one degree of freedom comprises anchoring the at least one nozzle to substantially align a longitudinal axis of a nozzle assembly including the at least one nozzle with a longitudinal axis of the bore of the structural element.
 60. The method of claim 58, further comprising rotating the nozzle assembly about a longitudinal axis of the bore of the structural element.
 61. The method of claim 58, wherein forming at least one fluid cutting jet comprises forming at least one substantially circumferential fluid cutting jet. 